1. Field of the Invention
The present invention relates to a leakage current compensation circuit configured to compensate for a leakage current of a MOS transistor, and to a semiconductor device.
2. Description of the Related Art
In a circuit including a MOS transistor, in general, circuit constants are determined to design electrical characteristics of the circuit after modeling the MOS transistor as an ideal element without leakage current. However, in an actual MOS transistor, there are parasitic diodes between a source and the bulk and between a drain and the bulk. A reverse leakage current of the parasitic diode, which increases especially at high temperature, deteriorates electrical circuit characteristics. Further, a leakage current from a gate of the MOS transistor also deteriorates electrical circuit characteristics.
FIG. 4 is a circuit diagram of a related-art leakage current compensation circuit.
The related-art leakage current compensation circuit is configured to compensate for a reverse leakage current IL of a parasitic diode 411 of a MOS transistor 401 which has a drain to which a circuit 20 is connected and a gate to which a circuit 30 is connected.
Since reverse bias voltage is applied between the drain and the source of the NMOS transistor 401, in the parasitic diode 411 of the MOS transistor 401, the reverse leakage current IL flows to the bulk of the MOS transistor 401. As a result, a current flowing to the circuit 20 increases by an amount of the reverse leakage current IL. The reverse leakage current IL is a current error with respect to the operating current of the circuit 20, and hence deteriorates circuit performance.
The leakage current compensation circuit includes a MOS transistor 402 configured to generate, as a compensation current, a reverse leakage current IC of a compensation diode 412, and a current mirror circuit which includes MOS transistors 403 and 404 configured to supply, to the MOS transistor 401, an output current with use of the compensation current IC as an input current. The MOS transistor 401 and the MOS transistor 402 are transistors of the same type and the same size due to a process structure, and a gate of the MOS transistor 402 is connected to a ground terminal VSS so that the MOS transistor 402 is set to be in an OFF state. Thus, the reverse leakage current IC of the compensation diode 412 and the reverse leakage current IL of the parasitic diode 411 become equal to each other in magnitude. Accordingly, the reverse leakage current IL generated in the MOS transistor 401 is compensated for by the leakage current compensation circuit (for example, see Japanese Patent Application Laid-open No. Hei 8-340246).
However, in the related-art leakage current compensation circuit, it is required that the compensation MOS transistor 402 have the same size as that of the MOS transistor 401 in order to generate a compensation current IC having the same magnitude as that of the reverse leakage current IL, which is generated in the MOS transistor 401 and is to be compensated for. Accordingly, an area of the layout pattern greatly increases.
Further, compensation of the leakage current is limited to a reverse leakage current of a diode, and a leakage current from a gate, which tends to increase accompanying with miniaturization in the manufacturing process, cannot be compensated for.